A typical aerofoil structure, e.g. for aircraft, comprises a torsion “wing box” having front and rear longitudinal spars, a plurality of transverse ribs attached to the front and rear spars and upper and lower covers extending between the front and rear spars. A plurality of longitudinal stringers are typically attached to or integrally formed with the covers to stiffen and strengthen the covers so that the thickness, and therefore weight, of the covers can be reduced. The ribs, spars and covers, and sometimes also the stringers, are each manufactured as separate components which are fastened or otherwise fixed together to form the aerofoil structure.
Over recent decades there has been a move towards greater use of composite materials in aerofoil structures to replace traditional metallic materials with the aim of reducing structural weight. Commonly used composite materials includes fibre reinforced polymer laminates, such as carbon fibre reinforced polymers. Currently, composite aerofoil structures are generally similar in design to the metallic structures which they have replaced, having stringers attached to or formed with covers, which are bolted or bonded to the spar and rib components.
To date, composite materials have not fulfilled their potential, to the extent that hybrid structures including composite and metallic components (e.g. metallic ribs with composite spars and composite covers) have been shown to sometimes be superior to all composite structures. The direct replacement of metallic components with similar components formed using composite materials often fails to make the most efficient use of composite materials. Known composite, or hybrid, aerofoil structures are therefore not optimised and have a large number of components. The direct replacement of metallic components with similar composite components also fails to maximise the properties and manufacturing processes which are possible with composite materials.